What is the most common cause of a scrotal mass?
A spermatocele or an epididymal cyst is the most common cause of a scrotal mass. Spermatoceles contain spermatozoa, whereas epididymal cysts do not. However, these are indistinguishable on imaging. On US, a well-circumscribed anechoic cystic lesion with posterior acoustic enhancement is seen in the epididymis, without blood flow on Doppler US. On CT and MRI, a nonenhancing well-circumscribed cystic lesion is seen in the epididymis. Internal septations or complex fluid may sometimes be present.
Tubular ectasia of the rete testis is associated with spermatoceles and epididymal cysts, as well as with advancing age and a history of prior vasectomy. It is secondary to partial or complete obliteration of the efferent ductules. On cross-sectional imaging, multiple tubular cystic structures are seen in the region of the mediastinum testis, often within both testicles, without mass effect. No blood flow is seen on Doppler US, and no enhancement is seen on CT or MRI.
Testicular cysts can also occur, which have similar cross-sectional imaging features as those of spermatoceles and epididymal cysts except for having a location within the testicle. They are benign, are more commonly encountered with increasing age, and are typically seen near the mediastinum testis
